Tire shredding machines are employed to reduce tires, particularly automotive tires, to small pieces of rubber which can be reused in manufacturing a variety of products. Several different machines are used to reduce tires, but most are rotary shredders of the type shown in U.S. Pat. No. 6,343,755 to Barclay and Diemunsch, incorporated by reference herein. In the first stage of tire reduction, a primary shredder is used to digest a whole tire and reduce the tire to oddly shaped pieces of rubber. From these oddly shaped pieces, rubber is subsequently reduced in secondary and tertiary shredders to finer and finer pieces of rubber until the rubber reaches the desired size, sometimes as fine as granular pellets or even small sawdust-like particles. However, the initial burden of tire reduction is placed on the primary shredder which must deal with the toughness and strength inherent in tire body construction.
In the early days of primary shredder construction, rotary shears were designed wherein a pair of counter-rotating, intermeshing, serrated cutting wheels, mounted on parallel rotating hubs or shafts, received a tire at a zone of intermeshing and proceeded to digest a tire by ripping the tire into strips which could pass between the wheels and be ejected after passage. The number of pairs of parallel cutting wheels on a single shaft or hub could vary, but usually more than six and less than twenty cutting wheels were placed on a single hub, with parallel wheels separated by spacers to allow intermeshing of another set of parallel wheels on another hub. A large number of parallel cutting wheels increases the size and number of tires which can be accepted into the machine for digestion.
Some strips of rubber would become jammed between adjacent cutting wheels during digestion and needed to be removed by a fixed tool, so that a clear zone of intermeshing would be presented to a tire upon rotation of the wheel. At the zone of intermeshing, a tire would encounter the outer periphery of counter-rotating cutting wheels. After continuous rotation for a period of time, the outer periphery of the cutting wheels would become worn, mainly at the outer periphery, by the toughness of tires and the wheel would need to be resurfaced. The problem of resurfacing cutting wheels has been addressed by several inventors. The above-mentioned '755 patent teaches that the outer peripheral contact region of a cutting wheel may be removed so that the entire cutting wheel need not be removed from its shaft for repair. Rather, by refinishing or replacing the outer contact region, a certain amount of modularity can be introduced which eases maintenance. The principle of modularity was extended by Bernhardt et al. in U.S. Pat. No. 5,318,231 wherein cutter wheels were provided with removable peripheral contact regions and adjacent wheels were laterally paired and joined on opposite sides of a spacer, in a sandwich construction. Now, each cutting wheel is actually a pair of wheels, separated by a spacer wheel, in relation to a shaft on which the wheels are mounted. This facilitates maintenance and assembly of both cutting surfaces and the wheels themselves. Paired cutting wheels are accurately spaced in relation to each other.
In summary, the prior art recognizes that wear in cutting wheels occuring at outer periperal surfaces contacting tires to be shred can be offset by removing and replacing or refinishing the outer wear surfaces, thereby obviating the need to remove an entire cutting wheel and facilitating maintenance. The prior art also recognizes that modularity may be employed not only by providing replaceable cutting surfaces, but also in wheel construction by pairing cutting wheels with an intermediate spacer wheel in a sandwich construction. An object of the invention was to facilitate maintenance in cutting wheels of rotary shearing apparatus by improving modular construction of cutting wheels.